DESCRIPTION: (Applicant's Description) The overall goal of the proposed research is the development of applicators for precise delivery of high intensity ultrasound to regions of the prostate containing cancer, with concurrent real-time thermal monitoring of the prostate and periprostatic tissues. The project represents a collaborative effort in which high-intensity applicators suitable for transurethral and interstitial use will be fabricated at University of California at San Francisco, and then tested in the in vitro and in vivo MRI studies by investigators at Stanford University. Three types of catheters suitable for transurethral use, differing in their degrees of acoustic focusing will be designed, fabricated and tested in the in vitro studies, these studies will determine the most promising design for practical prostate ablation. Evaluation criteria will include the speed of heating possible, the ability to perform conformal delivery of heating to desired regions, and ease of use. The most promising design or designs will then be tested in vive in a canine animal model with MR/ thermometry using phase-sensitive imaging. Correlative thermocouple measurements will be made during these studies, and a real-time thermometry reconstruction and display systems developed at Stanford will be adapted for thermal mapping of the prostate. Histologic studies of the in vive insonated prostatic and periprostatic tissues will be performed, and correlated to phase-sensitive, T2-weighted and contrast enhanced MR images, to determine the most effective procedure for imaging prostate tissue necrosis directly with MRI.